The present invention relates to a method and apparatus for metal deposition. More particularly, the present invention relates to a method and apparatus for depositing metal onto the edge of a thin metal substrate.
Current techniques for depositing metal onto thin edge substrates include arc processes using filler wire and laser processes using metal powder. Such techniques are frequently used to repair components found in modern gas turbine engines. These components are subjected to extreme conditions which can cause mechanical and thermal damage, usually in the form of cracking or abrasion wear, which often occurs in specific regions. Due to the extreme operating conditions, these components are highly complex and expensive to manufacture. The replacement costs for these parts are extremely high and, in most cases, repair is a more viable solution.
The repair process typically involves: excavating the damaged region using a machining or a grinding process, replacing the excavated material (typically by melting a suitable filler metal and fusing it to the part being repaired), and then shaping the deposited metal to resemble the geometry of the original part. Replacement of the excavated material is conventionally performed using either the arc-and-wire process (e.g., gas tungsten arc welding (GTAW) or plasma arc welding (PAW)) or laser-and-powder process mentioned above. Although these methods are suitable for material deposition, both have certain limitations.
For example, GTAW and PAW processes induce substantial heat into the part being repaired, which can adversely affect the metallurgy. To eliminate this problem, complex chills are used to cool the parent material. In addition, the weld bead profile is relatively difficult to control, resulting in a substantial amount of material that needs to be removed during the final shaping process. An example of an arc-and-wire process is disclosed, e.g., in U.S. Pat. No. 4,418,266, which is hereby incorporated by reference herein its entirety.
The laser-and-powder process (which uses a laser in combination with metal powder used as a filler) has a lower heat input and can produce xe2x80x9cnear-netxe2x80x9d geometry. Examples of a laser-and-powder process are disclosed, e.g., in U.S. Pat. Nos. 6,326,585 and 6,476,343, which are both hereby incorporated by reference herein in their entirety. However, the metallurgical properties of the resulting deposit are often inferior to those generated by an arc process. For example, the level of porosity is often too high to meet specifications. In addition, some of the powder misses the weld pool, commonly referred to as xe2x80x9coversprayxe2x80x9d, resulting in wasted material and potential damage to the substrate.
Over the years, material joining and cladding operations have been conducted using a third technique, referred to as a xe2x80x9claser-and-wire processxe2x80x9d. Example of laser-and-wire processes are disclosed, e.g., in U.S. Pat. No. 5,578,227 (which uses flat wire) and in on-line articles: xe2x80x9cProduction of 3-D Structures with High Strength-to-Weight Ratiosxe2x80x9d (found at the website http://wvww.hrtechnology.com/new page 4.htm) and xe2x80x9cThe Paradigm Shifts: Net-Shape Manufacturingxe2x80x9d (found at the website http://www.ndx.com/printpage.asp?article id=373). The foregoing references are hereby incorporated by reference herein in their entirety.
In material joining processes, wire is commonly used to fill the space between two or more elements being welded together or as an alloying element. An example of a material joining process is disclosed, e.g., in U.S. Pat. No. 5,532,454, which is hereby incorporated by reference herein in its entirety.
In cladding processes, a filler wire is melted to create a relatively thin, homogenous layer of metal. An example of a cladding process is disclosed, e.g., in U.S. Pat. No. 5,889,254, which is hereby incorporated by reference herein in its entirety.
The layer formed by a cladding or material joining process can be used to replace worn-out material in repair applications or to create a coating with specific properties such as corrosion or wear resistance.
Metal deposition onto a thin edge of a metal substrate differs substantially from cladding applications. In thin-edge applications, the object is to generate a xe2x80x9chighxe2x80x9d deposit (i.e. a deposit having a high height-to-width ratio, also referred to as a high aspect ratio), rather than a flat layer. This presents several difficulties which are not present in cladding. For example, a thin edge does not provide a good heat sink for the weld pool. As a result, the weld pool temperature and, consequently, the weld pool size must be minimized in order to prevent excessive melting of the substrate. However, decreasing the temperature and size of the weld pool narrows down the parameter range in which a successful deposition can be achieved. Of particular importance is the relation between the heat sink properties of the substrate, the power input rate and the wire feed rate. Surprisingly, the relationship between the distance from the wire nozzle to the weld pool and the wire diameter is also critical. This relationship has been overlooked in the past, resulting in wire entry control problems.
Thus, it is continually desirable to provide a method and apparatus for depositing metal onto a thin edge of a metal substrate, which provide a deposit having a high aspect ratio, a xe2x80x9cnear-netxe2x80x9d geometry and good metallurgical properties, which is achieved without excessive waste of material or the use of chills.
The present invention provides a method and apparatus for depositing a metallic material onto a thin edge of a metal substrate (also referred to herein as a xe2x80x9cthin-edge metal substratexe2x80x9d), wherein the invention eliminates the problems associated with the laser-and-powder and arc-and-wire processes described above. Instead of using an arc-and-wire process or a laser-and-powder process, the instant invention uses a xe2x80x9claser-and-wirexe2x80x9d process to deposit metal onto a thin-edge substrate. As noted above, laser-and-wire processes have been used in material joining and cladding operations. However, as was further pointed out above, material joining and cladding operations differ significantly from thin-edge deposition operations, the latter operations involving challenges not encountered in the former operations.
The present invention overcomes the problems associated with the arc-and-wire and laser-and-powder processes. As noted above, both of these techniques suffer from problems that are difficult to overcome. The arc-and-wire process induces substantial heat into the substrate which creates a requirement for cooling. The deposits produced using the laser-and-powder process often suffer from inferior metallurgical quality. This process also creates problems with metal deposition inefficiencies and xe2x80x9coversprayxe2x80x9d.
The present invention is based on the discovery that the laser-and-filler process of this invention can effectively deposit metal onto a thin-edge metal substrate without the problems associated with the arc-and-wire and laser-and-powder processes.
The present invention is directed to a method of depositing metal onto an edge of a metallic substrate, involving
(1) directing a high intensity light beam onto the substrate, thereby melting a portion of the substrate and forming a weld pool;
(2) while directing the light beam onto the weld pool, introducing a filler wire into the weld pool, wherein exposure to the light beam and residual heat in the weld pool causes the filler wire to melt into the weld pool, the light beam providing sufficient energy to fuse the molten filler wire to the substrate;
(3) feeding the filler wire into the weld pool while effecting relative motion between the filler wire and the light source relative to the substrate such that a continuous weld bead is formed from the weld pool;
(4) optionally adjusting tiller wire feed rate, light source output, weld velocity and relative movement between the substrate and the light source during deposition to compensate for variations in substrate thickness; and
(5) during steps (1)-(4), exposing the weld pool and filler wire disposed therein to a shielding gas so as to protect the weld pool and filler wire from oxidation.
The method of this invention is preferably carried out by a metal deposition apparatus composed of:
(a) a high intensity light source for melting a portion of the substrate to form a weld pool;
(b) a filler delivery system for continuously delivering a filler wire to the weld pool;
(c) a motion system for effecting relative motion between the substrate and the light source;
(d) a shielding gas delivery system for delivering a shielding gas to a position such that the shielding gas protects the weld pool and filler wire disposed in the weld from oxidation; and
(e) means for adjusting process and motion parameters to compensate for variations in substrate thickness.
The metal deposit achieved by the present invention is characterized by a relatively high height-to-width ratio (also referred to as xe2x80x9caspect ratioxe2x80x9d). The aspect ratio can be further enhanced by depositing several beads of metal on top of each other.
The weld bead profile and metallurgical properties can be controlled by varying process parameters such as speed, power input and wire feed rate.
The method and apparatus of the present invention can be used in any application which requires metal deposition, particularly applications wherein specific properties and geometries of the deposited metal are required. When used to repair components found in modern gas turbine engines, the present invention avoids the problems associated with conventional repair techniques, discussed above, and achieves xe2x80x9cnear-netxe2x80x9d geometry and good metallurgical quality without the use of chills or excessive waste of material.